General oligosaccharide synthesis can be performed only when stereoselective glycosylation is possible. In general, the anomeric position can be selected by optimizing reaction conditions, such as solvent, temperature, promoter, leaving group, and protecting group patterns. At present, stereoselective synthesis of 1,2-cis-glycoside is a complicated oligosaccharide synthesis challenge. Concerning proceeding of the 1,2-cis-stereoselective glycosylation of 2-amino-2-deoxysugar, in particular, Lemieux and Paulsen reported about 30 years ago the introduction of an azide group into position 2 as a protecting group that is not involved with an adjacent group (H. Paulsen, et al., Chem. Ber., 1978, 111, 2358-2369 and R. U. Lemiuex, et al., Can. J. Chem., 1979, 57, 1244-1251). According to the method of Lemieux and Paulsen, the 1,2-cis-form is preferentially synthesized, but satisfactory selectivity is not always realized. Also, sugar donor synthesis disadvantageously involves the employment of a special technique referred to as azidonitration, or the use of triflic azide, which causes danger of explosion.
In 2001, Kerns reported that a sugar donor having 2,3-trans-oxazolidinone exhibited high selectivity (K. Benakli, et al., J. Am. Chem. Soc., 2001, 123, 9461-9462). However, this sugar donor is reported to have several drawbacks (P. Wei, et al., J. Org. Chem., 2005, 70, 4195-4198 and P. Wei, et al., Tetrahedron Lett. 2005, 46, 6901-6905). First of all, at least 2 equivalent amounts of activators (phenylsulfenyl triflate) are required. Also, sulfenylation and glycosylation at nitrogen atom are severe side reactions. When a nitrogen atom is subjected to acetylation, selectivity is significantly decreased, although β-selectivity is occasionally observed. In the case of a sugar donor using an acetamide group as an amino-protecting group, deprotection of trans-oxazolidinone at 2,3-positions is problematic under basic conditions. That is, hydrolysis of the trans-oxazolidinone structure is intended while maintaining an acetamide group. However, such hydrolysis disadvantageously competes with acetamide hydrolysis, which makes performance of selective hydrolysis difficult and which results in formation of various products in some cases.